The present invention relates to a method of manufacturing a magnetic thin film medium with controlled grain morphology and topology. More particularly the invention is directed to a magnetic medium in which a magnetic thin film is deposited on a thin transient liquid metal layer deposited onto a non-wettable substrate, the surface topology and magnetic characteristics of the medium being controlled by adjustment of the thickness of the transient liquid metal underlayer and the deposition conditions.
The demand for increased capacity of storage media has resulted in the development of the magnetic thin film disk. The magnetic thin film disk should have a high and controllable coercivity, preferably in the range between 600 and 2000 Oe, and a high remanent magnetization. Binary or ternary cobalt-based alloys, such as CoCr, CoRe, CoPt, CoNi, CoNiCr, CoPtCr and the like are commonly used as the magnetic material in thin-film magnetic disk technology. Platinum is one of the key elements in achieving high coercivity, of greater than 900 Oe, required for disks. Depending upon the required range of coercivity, up to 20 percent of Pt can be added to Co based alloy.
The magnetic film is deposited on a non-magnetic substrate, typically NiP-coated Al-Mg or glass disks. The recording density of a medium is inversely proportional to the distance (fly height) between the disk and a magnetic head with which the information is being recorded. Thus the surface of the disk substrate should be extremely smooth to permit a lower fly height. However the extreme smoothness of the disk generally results in a high contact area between the disk and head which, in turn, results in a high value of stiction or friction. The high stiction or friction can cause damage to the disk, recording head and its assembly as well as disk drive motors. In order to alleviate the problem, an overcoat, typically carbon, as well as a lubricant are applied to the outermost film layer. However, extremely smooth disks even with a lubricant coating may still exhibit unacceptably high stiction and friction levels. Moreover, over a period of time the lubricant is removed from the disk surface. Therefore, a controlled surface topology or texture is required to enhance flyablility and lubricant retention.
In order to overcome the problems of high stiction and friction, prior to the deposition of the magnetic layer the surface of the disk substrate is roughened by one of the common mechanical abrasive techniques known as texturing.
The mechanical texturing usually is associated with the formation of weldments and asperities along the texture lines. These weldments can result in an increase in fly height as well as severe wear of the magnetic layer during operation of the disk. Therefore, it is desirable to texture or roughen the substrate surface by means other than mechanical abrasion while not adversely affecting the disk magnetic properties.
It is also desirable to enhance coercivity of the magnetic disks while reducing the quantity and expense of platinum element additions.
In U.S. Pat. No. 4,539,264 entitled "Magnetic Recording Medium" a magnetic recording medium is described as having a non-magnetic substrate, a bismuth layer of less than 100 .ANG. thick and a magnetic metal thin film formed on the bismuth layer. While the described medium achieves increased coercivity levels, the bismuth layer remains as a discrete underlayer and the topological and alloying effects resulting from a transient liquid metal layer are not achieved. The patent also fails to suggest the application of a layer of metal film between the bismuth layer and the magnetic layer which is an alternative embodiment of the present invention.